In a Long Term Evolution (LTE) in unlicensed spectrum (LTE-U) system, a base station uses a channel resource according to a listen before talk (LBT) rule. LBT is a carrier sense multiple access (CSMA) technology. In a process in which the base station sends data to user equipment by using a physical downlink shared channel (PDSCH), the base station needs to obtain channel state information (CSI) fed back by the user equipment. In the prior art, a licensed spectrum is used in an LTE system for a long time, and CSI is mainly fed back in a periodic or aperiodic manner during use of the licensed spectrum.
An aperiodic CSI feedback is triggered by using uplink signaling. In a data sending process of a base station, the base station controls, by using a CSI request report, user equipment to feed back CSI in uplink signaling, and a CSI feedback process has at least a 10-ms delay. A periodic CSI feedback is configured by using higher layer signaling, and this requires user equipment to initiate one CSI feedback to a base station at a particular time interval. However, in the LTE-U system, unlicensed spectrum is used at random. Therefore, if a CSI feedback mechanism in the LTE system is directly used in the LTE-U system, because the CSI feedback process has at least a 10-ms delay during the aperiodic CSI feedback, a real-time feedback of a CSI status cannot be ensured; and during the periodic CSI feedback, the CSI feedback causes signaling overheads when the base station has no data to be sent, thereby causing a resource waste.
In conclusion, no CSI status feedback mechanism suitable for the LTE-U system can be provided in the prior art.